The problem is to find how oxygenases work. Dioxygen, an essential cellular substrate, assumes multiple redox states. Some are stable, others labile, highly reactive, shortlived, and free radical. The ubiquitous P450 heme-thiolate monoxygenase center, on single polypeptide sequences, uses O2 and redox energy to hydroxylate hydrocarbons selectively. Alternatively, it uses H2O2, alkyl peroxides, peracids, or the single oxygen donor iodosobenzene. The question becomes: what are the intermediate states, which amino acids are essential to the heme-thiolate and substrate centers, and to the subunit domains? That is, how many P450 molecules are there, what are the reaction mechanisms, and the enzyme and substrate product intermediates? The measurements and theory promptly available from physics and chemistry provide access to primary reactions. Those perfected within the Illinois multidiciplinary effort and detailed in our collective papers range from genetic organization and the control of enzyme formation, to substrate modulation, turnover rates and specificity, and to the number of substrate pockets in the microbial and mitochondrial ternary systems. Among P450 proteins from divergent species, retained sequences imply common features as reflected to the resonance probes. With cloning, and the first primary and tertiary structures available, and with other P450 sequences now reported, pre- and post-transcription/translation modifications can be applied to identify essential functions. We are requesting support to complete the production, characterization, and comparison of the three P450 ternary systems; to identify the residues, coordinates and ions needed in binding, spin change, and catalysis, in common to all or specifically to individual P450 proteins. Our developments with the linalool-8, and p-cymene-10, methyl hydroxylases provide the additional rich resources needed to check the generality of the primary and tertiary structures given by the P450 cam model. Additionally, the aromatized p-cymene offers a bridge from aliphatic to aromatic metabolic patterns and the available analogues shed light anew on the functional group in question for nature's coping with structural variety.